抽象基类一般用于规定子类必须重新定义某些方法。比如 web 框架中的 cache 部分的基类一般类似下面这样:
class BaseCache(object):
def get(self, key):
raise NotImplementedError('subclasses of BaseCache must provide a get() method')
def set(self, key, value, timeout=60):
raise NotImplementedError('subclasses of BaseCache must provide a set() method')
class MemcachedCache(BaseCache):
def get(self, key):
value = self._cache ...sudo apt-get install postgresql-client sudo apt-get install postgresql
sudo service postgresql start
sudo -u postgres psql
或
psql -U dbuser -d exampledb -h 127.0.0.1 -p 5432
退出
postgres=# \q
sudo -u postgres createuser dbuser
或
sudo -u postgres psql postgres ...
两个模块间互相导入时，可能会出现如下的问题：
# a.py
from b import y
print y
x = 5
# b.py
from a import x
print x
y = 10
>>> import b
Traceback (most recent call last):
File "<stdin>", line 1, in <module>
File "b.py", line 1, in <module>
from a import x
File "a.py", line ...本文说的这几个问题适用于 python 2.6+ 。
In [1]: a = 1
In [2]: def func():
...: print(a)
...: a = 2
...:
In [3]: func()
---------------------------------------------------------------------------
UnboundLocalError Traceback (most recent call last)
<ipython-input-3-08a2da4138f6> in <module>()
----> 1 func()
<ipython-input-2-9e6cf545bc05> in func()
1 def func():
----> 2 print(a)
3 a ...系统: CentOS
修改 vsftpd.conf，启用被动模式，指定端口:
pasv_min_port=12000 pasv_max_port=12199 pasv_enable=YES
配置防火墙 iptables，允许端口访问:
iptables -I INPUT -p tcp --dport 12000:12199 -j ACCEPT service iptables save